This relates to a computer output printer of the dot matrix type and in particular to a method and apparatus for accessing the individual printing elements in a printhead matrix.
In one type of dot matrix printer a line of closely spaced printing elements extends across the surface of a recording medium. In order to print alphanumeric characters of reasonably good visual quality, the printing elements may be arranged in a density of as many as 100 per linear inch. Typically, these printing elements are individually addressed by a printhead control that includes two sets of electrically conductive leads with one lead from each set being connected in series to each printing element but each such pair of leads being different. To print a dot on a recording medium such as thermal paper, the printhead control applies a voltage source to one of the two leads while the other lead is grounded. A current flow for about two to five milliseconds is sufficient with presently available printing elements to heat the region of the thermal paper adjacent the printing element enough to form a dot thereon.
While such writing speeds appear relatively fast, a large number of dots are required to make up a character. Typically 5.times.7 and 7.times.9 dot matrices are used and there can be 400 or more printing elements across a four inch wide strip of paper. Efforts to increase printing speeds, moreover, are complicated by the wiring patterns used to access the printing elements. Such patterns appear to be designed to minimize lead lengths and interconnections so as to reduce resistive losses and faults. Little attention appears to have been given to organizing the printhead control for maximum print speed.